This invention concerns therapeutic radiation treatment of living tissue, usually but not necessarily within a body cavity, which may be a surgical cavity following a resection of a tumor. In one aspect the invention is concerned with use of a switchable, miniature electronic x-ray source, which may be controllable as to depth and intensity, for administering such therapeutic treatment.
Treatment of surgical cavities, such as after malignant tumor excision, has been accomplished with applicators which are inserted usually into a newly formed opening through the skin, a conveniently located opening into the surgical resection cavity. Generally the location is different from the surgical closure itself. Applicators have been disclosed which essentially comprise a balloon of known and relatively rigid geometry, essentially spherical, expandable generally to about four to six centimeters, that is, designed to have an inflated size of about four to six centimeters diameter. Some of the generally spherical balloon catheters were described as having multiple walls to form inner and outer spaces, for reasons relating to the objective of delivering a uniform dose to tissue surrounding the balloon. In the prior art such known-geometry balloons were inflated with a liquid, with an applicator guide positioned within the balloon and in the liquid, so that the applicator guide could receive a radiation source comprising a radioactive isotope.
With balloons limited to known geometries, there are limitations in the ability to treat a cavity margin thoroughly. In some cases, the patient cannot take advantage of such a treatment protocol because the known-geometry balloon applicator simply cannot fill many surgical cavities that are irregular in shape. Other measures have to be used in those cases, such as external radiation therapy.
Another limitation of known procedures using balloon catheters is in regard to locating the balloon correctly within a cavity of the patient, such as a resection cavity. The saline solution used to inflate the balloon contains contrast material which will be visible by taking an external x-ray. With the contrast material contained in the balloon's solution, the surgeon or technician can detect a pale “shadow” in the x-ray to determine the location of the balloon and to correct its position if needed. The procedure typically calls for use of the contrast material at about 3% in the saline solution. Dose planning for the known-geometry balloon is based on specific concentration of contrast. However, because the balloon shape is difficult to see in the x-ray, surgeons usually add the contrast material in a much higher concentration, not as contemplated by the dose plan, so as to better detect the balloon in the x-ray. The concentration may be up to about 20%-30% in practice. As a result, the therapeutic radiation from the x-ray source placed into the center of the balloon becomes attenuated to the extent that the actual dose profile received in a patient's tissue may be significantly less than the prescribed dose.
The use of isotopes has been the practice in administering x-ray radiation to patients prior to the present invention. The isotopes must be handled carefully and reliably shielded between uses. With the isotopes they are always “on”, and only one setting is available for all dwell locations where a dose is to be administered. In many cases it would be convenient to have a better procedure and source that would allow modulation and more accurate dose delivery.